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Bartz, M.*; King, G. E.*; Bernard, M.*; Herman, F.*; Wen, X.*; 末岡 茂; 塚本 すみ子*; Braun, J.*; 田上 高広*
Earth and Planetary Science Letters, 644, p.118830_1 - 118830_11, 2024/10
被引用回数：1 パーセンタイル：27.39(Geochemistry & Geophysics)The impact of climate on mountain relief is unknown, mainly due to the difficulties of measuring surface processes at the timescale of glacial-interglacial cycles. An appropriate setting for studying mountain erosion in response to Quaternary climate change is found in the Tateyama mountains in the Hida mountain range (northern Japanese Alps) due to distinct geomorphological features of glacial, periglacial, and fluvial processes. The Japanese Alps uplifted within the past ca 1-3 Myr and experienced multiple glaciations during the late Quaternary. We use ultra-low temperature thermochronometers based on the luminescence of feldspar minerals and the electron spin resonance (ESR) of quartz minerals, in combination with inverse modelling to derive rock cooling rates and exhumation rate histories at 10
-10
year timescales from 19 rock samples from three transects in the Tateyama region. While luminescence signals have already reached their upper dating limit, ESR signals (Al and Ti centres) yielded ESR ages of ca 0.3-1.1 Ma, implying surface processes active in the Pleistocene. Based on a negative age-elevation relationship, local relief reduction at a cirque-basin scale is identified over the past 1 Myr, whereas a positive age distribution with elevation for samples close to the mountain top does not follow this trend. Inverse modelling reveals rock cooling rates on the order of 30-80 deg. C/Ma, with slightly faster cooling for cirque-floor samples, which equate with erosion rates of 0.5-1 mm/yr that exceed rates from periglacial and fluvial processes in the same locality. Thus, our data suggest that Quaternary climate change coupled with distinct surface processes modified the slopes of the Tateyama mountains leading to a localised decrease in relief over the second half of the Quaternary, whilst the mountain peaks were unaffected by the relief reduction.
第四紀深成岩体の固結年代・深度に基づいた飛騨山脈黒部地域の削剥史末岡 茂; 河上 哲生*; 鈴木 康太*; 鏡味 沙耶; 横山 立憲; 芝崎 文一郎*; 長田 充弘; 山崎 あゆ*; 東野 文子*; King, G. E.*; et al.
フィッション・トラックニュースレター, (36), p.1 - 3, 2023/12
飛騨山脈黒部地域には、世界一若い露出プルトンである黒部川花崗岩体を含め、10-0.8Maの若い深成岩体が複数露出する。深成岩体が一般に地下数km以深で形成されることを考えると、削剥速度は数mm/yrないしそれ以上に達する可能性がある。しかし、これらの若い岩体の貫入やこれに伴う熱水活動等の熱擾乱のため、熱年代法による、冷却史に基づく削剥史の復元は簡単ではない。本研究では、地熱条件に依らない削剥評価のため、主に鮮新世から第四紀の深成岩体の固結年代と固結深度から、黒部地域の削剥史の復元を試みた。固結年代はジルコンU-Pb年代測定法、固結深度はAl-in-Hbl地質圧力計により推定した。計14試料から固結年代と固結深度のペアを得た結果、固結深度は約6-10kmでほぼ均一で、東西及び南北のいずれにも系統的な変化を示さなかった。この結果は、黒部-高瀬川破砕帯の東側の断層ブロックが、東に傾動したと考える従来のモデルとは不調和である。固結深度と固結年代のプロットから復元された削剥史は、約5.5-0.8Maにはほとんど削剥が起こらず、それ以降の時代に平均で約7-14mm/yrの急速な削剥が起こったことを示した。この結果は、ダム堆砂量や宇宙線生成核種法から推定された数十から数千年程度の侵食速度や、約1Ma以降に信濃大町方面で黒部地域からの花崗岩礫の供給が急増したことと矛盾しない。0.8Ma以降の黒部地域の急速な隆起・削剥の原因としては、東西圧縮応力の発現以降、黒部地域の地温が高い領域に沿って変位・変形が局在化した可能性が考えられ、現在、レオロジーと地温構造を考慮した変形シミュレーションによる検証を進めている。
King, G. E.*; Ahadi, F.*; 末岡 茂; Herman, F.*; Anderson, L.*; Gautheron, C.*; 塚本 すみ子*; Stalder, N.*; Biswas, R.*; Fox, M.*; et al.
Geology, 51(2), p.131 - 135, 2023/02
The exhumation of bedrock is controlled by the interplay between tectonics, surface processes, and climate. The highest exhumation rates of centimeters per year are recorded in zones of highly active tectonic convergence such as the Southern Alps of New Zealand or the Himalayan syntaxes, where high rock uplift rates combine with very active surface processes. Using a combination of different thermochronometric systems including trapped-charge thermochronometry, we show that such rates also occur in the Hida Mountain Range, Japanese Alps. Our results imply that centimeter per year rates of exhumation are more common than previously thought. Our thermochronometry data allow the development of time series of exhumation rate changes at the time scale of glacial-interglacial cycles, which show a fourfold increase in baseline rates to rates of 10 mm/yr within the past 65 k.y. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting, and moderate rock uplift. Our data resolve centimeter-scale sub-Quaternary exhumation rate changes, which show that in regions with horizontal convergence, coupling between climate, surface processes, and tectonics can exert a significant and rapid effect on rates of exhumation.
河上 哲生*; 末岡 茂; 横山 立憲; 鏡味 沙耶; King, G. E.*; Herman, F.*; 塚本 すみ子*; 田上 高広*
Island Arc, 30(1), p.e12414_1 - e12414_11, 2021/01
被引用回数：4 パーセンタイル：19.34(Geosciences, Multidisciplinary)Solidification pressure and crystallization age of the ca 5 Ma Shiaidani Granodiorite (Hida Mountain Range, central Japan) are determined based on Al-in-hornblende geobarometry and U-Pb zircon dating. Al-poor patchy replacements developed in amphiboles are common in this granite and petrographic study revealed that the replacements include chloritized biotite and albitic plagioclase. These are probably the hydrothermally recrystallized domains, and should not be used for solidification pressure estimates. Magmatic rim of amphibole is characterized by Si 
7.3 a.p.f.u. (AlIV 
0.7 a.p.f.u.), and utilized in solidification pressure estimate that yielded 0.17-0.29 GPa. The solidification age of the granite is estimated as ca 5.6-5.2 Ma using U-Pb zircon dating. From these data, the lower limit of an average denudation rate after ca 5.6-5.2 Ma for the area where Shiaidani Granodiorite is exposed is estimated as 0.93-2.5 mm/year.
King, G. E.*; 塚本 すみ子*; Herman, F.*; Biswas, R. H.*; 末岡 茂; 田上 高広*
Geochronology (Internet), 2(1), p.1 - 15, 2020/01
石英の電子スピン共鳴(ESR)法は、岩石の冷却史の推定に有効な可能性が示唆されていたが検証が不十分だった。本研究では飛騨山脈の試料を用いてESR熱年代法の検証を行った。Al中心とTi中心の熱安定性は従来の予想より低く、長石のルミネッセンスと同程度と推定された。ESRデータから推定された熱史は、同じ試料のルミネッセンスデータから推定された熱史と同様のパターンを示した。一方、ESRの方がより長期間の熱史を復元することができ、石英のESR熱年代法が第四紀後期の地形発達史の解明に広く有用である可能性が示された。
Thiel, C.*; 塚本 すみ子*; 徳安 佳代子; Buylaert, J.-P.*; Murray, A. S.*; 田中 和広*; 白井 正明*
Quaternary Geochronology, 29, p.16 - 29, 2015/08
被引用回数：14 パーセンタイル：36.75(Geography, Physical)第四紀後期の隆起特性を評価するためには、堆積物の年代決定が重要である。本研究では、秋田県男鹿半島の海岸沿いの海成堆積物を用いて、堆積物中の石英および長石に対するルミネッセンス年代測定法の適用性について検証した。石英は、熱に不安定で、Linear modulated (LM)-OSL分析よりslow成分が卓越していることが示された。また、石英からは、堆積物に挟在する2つのテフラの年代と比較して、非常に若い年代値が得られた。カリ長石は、ドーズリカバリーテスト等の結果、225
Cのpost-IRIRSL信号を用いた場合に年代測定に適した鉱物であることが示されたが、篩い分けた粒径を基とした年間線量を年代値の算出に用いたところ、テフラの年代よりも若干、若い年代値が得られた。SEM解析により、長石粒子は小さな結晶を含んだ非晶質なものであることが分った。この場合、標準的な内部線量率を用いると、年間線量を過大に見積ることになる。そこで、以下の3つの年間線量のシナリオについて検討した。(1)篩い分けた粒径サイズ(90-180
m)で、カリウム(K)の含有量が12.5
0.5%、(2)SEM画像を基にした小さい粒径サイズ(4020m)で、Kの含有量が60.5%、(3)小さい粒径サイズ(4020m)で、Kの含有量が12.50.5%。その結果、(3)のシナリオがテフラ年代と最も調和的な年代値であった。
King, G.*; 末岡 茂; 塚本 すみ子*; Herman, F.*; Ahadi, F.*; Gautheron, C.*; Delpech, G.*; 田上 高広*
no journal, ,
熱年代学は、岩石の冷却速度を測定することで、削剥速度の推定が可能な手法である。近年発展したルミネッセンス熱年代は、光ルミネッセンス年代測定法を基にした手法で、100度以下の超低温領域の熱史の解明に加えて、1万年から10万年オーダーの時間スケールへの適用が可能である。本手法を飛騨山脈の基盤岩類に適用したところ、過去20万年間において約400度/100万年の急激な冷却が推定された。これらのデータを、先行研究によるより高温領域の熱年代学的データと組み合わせることで、より詳細な地形発達史の解明が期待できる。
King, G.*; 末岡 茂; 塚本 すみ子*; Herman, F.*; Ahadi, F.*; Gautheron, C.*; Delpech, G.*; 田上 高広*
no journal, ,
飛騨山脈は最近約1Maに急速に隆起したフェーズを持っていると考えられているが、この時代には氷期-間氷期サイクルが卓越している。本研究では、極めて低い閉鎖温度を持つ2種類の熱年代学的手法(ルミネッセンス熱年代、電子スピン共鳴熱年代)を飛騨山脈で採取した19点の基盤岩試料に適用し、第四紀後期の削剥史の推定を試みた。両手法とも共通して、最近10万年間は急速な冷却を示した。地温勾配を60度/kmと仮定すると、削剥速度はMIS4には約10mm/yrだったのが、最近2万年間には約1-3mm/yrに減少しており、氷河侵食による影響が示唆された。
King, G.*; 末岡 茂; 塚本 すみ子*; Herman, F.*; Ahadi, F.*; Gautheron, C.*; Delpech, G.*; 田上 高広*
no journal, ,
光ルミネッセンス(OSL)および電子スピン共鳴(ESR)熱年代は、近年発達した手法で、第四紀の侵食史の推定に有効である。本講演では、OSLおよびESR熱年代の概要と、日本アルプス北部の飛騨山脈における応用事例について紹介する。飛騨山脈は、世界で最も活動的な変動帯の一つである日本列島に位置し、3-1Ma以降に隆起したと考えらえている。基盤岩試料19点について両手法を適用したところ、100ka以降の急冷パターンが共通して得られた。地温勾配を60C/kmと仮定すると、削剥速度はMIS4では約10mm/yrであったが、過去20kaでは約1-3mm/yrに減少しており、寒冷・湿潤の気候下の方が侵食速度が速かったことが示唆される。
Bartz, M.*; King, G.*; Anderson, L.*; Herman, F.*; 末岡 茂; 塚本 すみ子*; Ahadi, F.*; Gautheron, C.*; Delpech, G.*; Schwarz, S.*; et al.
no journal, ,
Electron spin resonance (ESR) thermochronometry has the potential to resolve continuous erosion histories from rapidly eroding settings over 10 time scales. These time periods are defined by persistent oscillations between warm and cold states. However, questions about the relationship between climate and erosion remain unanswered. We further develop ESR thermochronometry of quartz (Al and Ti centres) to answer these questions in the Tateyama region in the Hida Mountains of Japan. In the result, the Al and Ti centres in quartz can successfully be inverted to unravel rock cooling histories. As future work, all ESR signals will be converted together with OSL data, providing further constraints on their thermal histories.
Bartz, M.*; King, G.*; Anderson, L.*; Herman, F.*; 末岡 茂; 塚本 すみ子*; 田上 高広*
no journal, ,
捕獲電子を用いた熱年代手法に基づいて、日本アルプス飛騨山脈の岩石試料を対象に冷却史の解明を試みた。
Bartz, M.*; King, G. E.*; Anderson, L.*; Herman, F.*; 末岡 茂; 塚本 すみ子*; 田上 高広*
no journal, ,
The Japanese Alps uplifted throughout the Quaternary and reached elevations of up to 3,000 m. However, understanding the interaction between rates of Earth surface processes, tectonics and climate is challenging, partly due to the difficulties of measuring changes in the rates of Earth surface processes at the timescale of glacial-interglacial cycles. In particular, the youth of the Japanese Alps has made measurement of their exhumation histories complicated. Here we investigate the potential of ultra-low temperature thermochronometers based on the luminescence and electron spin resonance (ESR) of feldspar and quartz minerals respectively for understanding changes in exhumation rates. We focus on Tateyama (Hida range), which was glaciated during the late Quaternary period. In total, eight samples were analysed by luminescence and ESR thermochronometry. While most luminescence signals have already reached their upper dating limit, ESR signals give insights into Pleistocene exhumation rates. We measured the ESR dose response and thermal decay properties of all samples, specifically targeting the Al and Ti centres. In general, thermal stability is higher for the Ti signals, resulting in ESR ages of between 0.5-0.9 Ma, although some signals are close to or above the upper dating limit of the Ti centre. In contrast, the Al signal still grows with time and is suitable for determining finite exhumation rates. Initial inversions reveal rock cooling rates on the order of 80 deg. C/Ma, which can be inverted to preliminarily rates of rock exhumation of <3 mm/a within the past 1 Ma. In the next step, we will relate these rates to the climatic (glacial) and tectonic history of the Tateyama region.
King, G. E.*; Ahadi, F.*; 末岡 茂; Herman, F.*; Anderson, L.*; Gautheron, C.*; 塚本 すみ子*; Stalder, N.*; Biswas, R.*; Fox, M.*; et al.
no journal, ,
The exhumation of bedrock is controlled by the interplay between tectonics, surface processes and climate. The highest exhumation rates of cm/yr are recorded in zones of highly active tectonic convergence. Here, we use a combination of different thermochronometric systems, and notably trapped-charge thermochronometery, to show that such rates also occur in the Hida Range, Japanese Alps. Our results imply that cm/yr rates of exhumation may be more common than previously thought. The Hida Range is the most northern and most extensive of the Japanese Alps, and reaches elevations of up to 3000 m a.s.l. The Hida Range is thought to have uplifted in the last 3 Myr in response to E-W compression and magmatism. Our study focuses on samples from the Kurobe gorge, which is one of the steepest gorges in Japan. Previous work has shown that exhumation rates in this region are exceptionally high, as documented by the exposure of the ~0.8 Ma Kurobe granite in the gorge. We combined 12 new zircon (U-Th/He) ages and 11 new OSL-thermochronometry ages together with existing thermochronometric data to investigate the late Pleistocene exhumation of this region. We found that exhumation rates increased to ~10 mm/yr within the past 300 kyr, likely in response to river base-level fall that increased channel steepness due to climatically controlled eustatic changes. Our data allow the development of time-series of exhumation rate changes at the timescale of glacial-interglacial cycles and show a four-fold increase in baseline rates over the past ~65 kyr. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting and moderate rock uplift. Our data show that in regions with horizontal convergence, coupling between climate, surface processes and tectonics can exert a significant effect on rates of exhumation.
Malatesta, L.*; 末岡 茂; 片岡 香子*; 小松 哲也; 塚本 すみ子*; Bruhat, L.*; Olive, J.-A.*
no journal, ,
On January 1st 2024, a Mw 7.6 earthquake shook the Noto Peninsula on the Sea of Japan coast of Central Japan. A large number of landslides and rockfalls dissected the road network. Liquefaction damaged infrastructure up to 150 km away from the epicenter. Meter-scale coseismic uplift modified the northern shoreline with displacement of the coastline by up to 200 m seaward discernible on SAR and aerial image data. At the time of abstract submission, we only have limited preliminary observations. It appears that the Noto Earthquake ruptured the same or adjacent fault to the May 5 2023 Mw 6.5 earthquake and was in the vicinity of the March 25 2007 Mw 6.9 Noto earthquake. Coseismic displacement measured geodetically shows uplift of up to +3-4 m (SAR) in the northwest of the peninsula, and +1.06 m (GPS) in the main town of Wajima-shi. The uplift magnitude decreases gradually to the SE. The uplift is near zero (SAR) or -0.3 m (GPS) on Noto Island 30 km to the south of the town of Wajima. Surface deformation goes back to near zero (GPS) a further 20 km to the south. The coseismic deformation pattern broadly reflects the deformation recorded in the Noto landscape. Long-term moderate rock uplift in the north gives way to a complex history of long-term slow uplift around Noto Island that likely includes sustained episodes of subsidence, highlighted by its sinuous "drowned" coastline. Along the western shore, marine terraces presumed to be 120 ka (last Interglacial) show a gradient in elevation also decreasing to the south. In the north, the newly emerged platform does not have a higher marine terrace counterpart. This may reflect the relationship between high wave power and moderate rock uplift resulting in the long-term retreat of the coastline and erosion of any terrace. The Noto Peninsula also holds widespread evidence of drainage reorganization that would reflect varying boundary conditions, in particular rock uplift, in deeper time beyond 100s ka.
Anderson, L.*; Bartz, M.*; King, G.*; Fox, M.*; Herman, F.*; Stalder, N.*; Biswas, R.*; 末岡 茂; 塚本 すみ子*; Ahadi, F.*; et al.
no journal, ,
Optically stimulated luminescence (OSL) and electron spin resonance (ESR) thermochronometry have the potential to resolve continuous erosion histories from rapidly eroding settings. These thermochronometers are viable over the past few hundred thousand to a million years. These time periods are defined by persistent oscillations between warm and cold states. During the Quaternary, fundamental questions about the relationship between climate and erosion remain unanswered. With further development, the OSL and ESR thermochronometers could answer these questions. To realize this potential new strategies are required to invert low-temperature thermal histories for erosion rates. Here, we explore the use of PeCUBE (Braun, 2003), a three-dimensional finite-element model that simulates heat conduction and advection in the upper crust. As a training dataset we use cooling histories derived from eight samples from the Tateyama region in the Hida Mountains of Japan. The flexibility of PeCUBE allows us to quantify the role of time varying surface temperatures between glacial and interglacial periods. In high-relief settings the three-dimensionality of the topography, for example between valleys and ridges, can substantially perturb rock temperatures. PeCUBE allows us to quantify and remove these confounding topographic effects. We additionally explore the role of changing topographic relief on time varying thermal fields and erosion rates. Lastly, we explore a generous range of model parameters to quantify the sensitivity and robustness of our inversions.
ne valley incision?King, G. E.*; Wen, X.*; Bartz, M.*; Anderson, L.*; Bossin, L.*; 塚本 すみ子*; Li, Y.*; Herman, F.*; 小形 学; 末岡 茂
no journal, ,
To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of geological samples including rocks from boreholes that have known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany) as well as samples from Sion in the Western European Alps. Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sub-linearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data. Inversion of two KTB samples yielded temperatures within uncertainty of borehole temperature, however results for the MIZ1 borehole are more variable and can only recover temperature at best within c.a. 10%. Investigations into the cause of the poor results for the MIZ1 borehole are ongoing (i.e. measurement protocol, data-fitting/numerical model) and will be discussed. Preliminary data from Sion are promising and reveal consistent cooling rates.
Bartz, M.*; King, G. E.*; Herman, F.*; Anderson, L.*; 末岡 茂; 塚本 すみ子*; 田上 高広*
no journal, ,
The interaction between rates of Earth surface processes, climate and tectonics determines the landscape in mountain regions. The Japanese Alps uplifted throughout the Quaternary and now reach elevations of up to 3,000 m. However, quantifying relief changes in response to tectonic activity, magmatism and Late Quaternary glaciation is challenging due to the young age of the Japanese Alps and the difficulty of measuring surface processes at the timescale of glacial-interglacial cycles. Here, we use ultra-low temperature thermochronometers based on the luminescence of feldspar minerals and the electron spin resonance (ESR) of quartz minerals, in combination with inverse modelling to derive rock cooling rates and time series of exhumation rates at 10-10 years timescales. We focus on the Tateyama region in the Hida range of the Japanese Alps, which was glaciated during the late Quaternary period. In total, 19 new samples were analyzed by luminescence and ESR thermochronometry. While most luminescence signals have already reached their upper dating limit, ESR signals (Al and Ti centres) yielded ESR ages of between 0.5-0.9 Ma. In general, thermal stability is lower for the Al centre compared to that of the Ti centre, but both centres constrain similar exhumation rates. Inversions reveal rock cooling rates on the order of 30-80 deg. C/Ma, which can be inverted to exhumation rates of less than 1 mm/a within the past 1 Ma. In the next step, we will relate the exhumation rates to the glacial and tectonic history of the Tateyama region.
Bartz, M.*; King, G. E.*; Herman, F.*; Anderson, L.*; 末岡 茂; 塚本 すみ子*; 田上 高広*
no journal, ,
To resolve exhumation histories of the Japanese Alps throughout the Quaternary, we investigate the potential of ultra-low temperature thermochronometers based on the luminescence of feldspar minerals and electron spin resonance (ESR) of quartz minerals, in combination with inverse modelling to derive rock cooling rates and exhumation rates histories at 10-10 years timescales. We focus on the Tateyama region in the Hida range of the Japanese Alps. In total, 19 new samples were analyzed by luminescence and ESR thermochronometry. While most luminescence signals have already reached saturation, ESR signals (Al and Ti centres) still grow with dose and are suitable for determining finite exhumation rates in the Tateyama region. We used the ESR single aliquot regenerative additive (SARA) dose protocol for dose evaluation including protocol optimization (i.e., preheat-plateau test). We checked for sensitivity changes due to the high-temperature annealing step within the SARA procedure using SARA vs. single aliquot additive dose response, repeated dose points (i.e., recycling ratio) and dose recovery of an artificially zeroed sample. Thermal stabilities of the ESR signals were analysed by using isothermal decay experiments and simulations of the isothermal decay using the experimentally constrained kinetic parameters. Our experiments showed insignificant sensitivity changes during measurements, resulting in Al and Ti ages of between 0.3-0.9 Ma and 0.5-1.1 Ma, respectively. In general, thermal stability is lower for the Al centre compared to that of the Ti centre but simulations yielded valuable thermal stability over Quaternary timescales for both ESR centres. Inversions reveal rock cooling rates on the order of 30-80 deg. C/Ma, much lower than those of the luminescence thermochronometry technique, which helps to resolve erosion rates histories on the order of few mm/a. Thus, preliminary erosion rates of 1 mm/a within the past 1 Ma could be inverted.
末岡 茂; 河上 哲生*; 鈴木 康太*; 鏡味 沙耶; 横山 立憲; 芝崎 文一郎*; 長田 充弘; 山崎 あゆ*; 東野 文子*; King, G. E.*; et al.
no journal, ,
Exposure of young ( a few Ma) plutons have been reported in mobile belts, such as, along subduction zones in the Western Pacific, implying a rapid exhumation in the last few million years. We reconstructed exhumation history of the Pliocene-Pleistocene plutons in the Kurobe area, central Japan, for better understanding of exhumation process and mechanism of such young plutons. Because low-temperature thermochronology is difficult to extract an exhumation history in the Kurobe area due to the complex thermal history/structure related to the recent granitic intrusions, we constrained the exhumation history based on solidification depths and dates of the plutons obtained by using Al-in-hornblende geobarometry and zircon U-Pb geochronometry, respectively. The solidification depths obtained range c.a. 6-10 km regardless of location and solidification age, suggesting a uniform and subvertical exhumation after the solidification of the youngest pluton (c.a. 0.8 Ma). The mean exhumation rate since c.a. 0.8 Ma was computed to be c.a. 7-14 mm/yr, which is consistent with the shorter-term erosion rates obtained by other methods. This rapid and local exhumation might be attributable to localization of deformation along the hot and weak crust along the Kurobe area related to the high-temperature geothermal conditions. This interpretation is being verified by using numerical modeling incorporating the rheology, geothermal conditions, and horizontal compression.
King, G. E.*; Wen, X.*; Bartz, M.*; Bossin, L.*; 塚本 すみ子*; Li, Y.*; Herman, F.*; 小形 学; 末岡 茂
no journal, ,
Whereas the luminescence thermochronometry system is limited to areas experiencing very rapid rock cooling (exhumation) of 10s of mm/yr, our data indicate that ESR thermochronometry can resolve rates of 1 mm/yr over Quaternary timescales. To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of borehole samples with known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models by using the ESR-thermochronometry method to recover their known in-situ temperatures. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany). Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double-exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sublinearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data.
